The invention is directed to a control system for load-independent distribution of a pressure medium to a number of different hydraulic energy consumers which are connected to one hydraulic pump and actuated by multiway valves. A pressure compensator for determining the flow of pressure medium to the multiway valve is installed upstream of each multiway valve and is actuated as a function of a first pressure differential derived from the pressure upstream of and the pressure downstream of the multiway valve and of a second pressure differential derived from the pump delivery pressure and the maximum consumer load pressure.
This type of controller is disclosed in German Patent DE-PS 34 22 165 and is particularly advantageous in combination with a load-sensing regulator. The pump usually has a discharge volume adjustment, which is load-sensing regulated. The load-sensing regulation creates a discharge volume adjustment of the pump as a function of the hydraulic energy required by the consumers. Thus, only the amount of pressure medium which is actually required is delivered by the pump so that circulation and throttling losses are minimized.
If no consumer is actuated because the multiway valves are closed, the pump is set for a slight delivery volume which only delivers overflow oil at a delivery pressure determined by a governor spring acting on a load-sensing regulator having two control pressure chambers. One control pressure chamber is acted upon by pump pressure and the other control pressure regulator is acted upon by the maximum consumer pressure and by the governor spring which provides a spring force equivalent to a pressure of 20 bar.
As long as no consumer is actuated and the control pistons inside the multiway valves assigned to the consumers are in the zero position, the pump will deliver only enough pressure medium so that the pump pressure on the load-sensing regulator equals the force of the spring on the opposite side of the load-sensing regulator to maintain equilibrium.
By displacing the control piston in a multiway valve, which is located ahead of a consumer, the pump is connected to that consumer, such that the pump pressure continues to that consumer. The displacement of the control piston in the multiway valve acts as a metering throttle. At the same time, the load pressure, namely the pressure in the line between the multiway valve which is actuated and the consumer being controlled, acts load-sensing regulator so that the pump receives a signal to increase the delivery volume and thus the pump pressure increase.
The consumer is then set in motion and a pressure gradient, .DELTA.p, is produced in the metering throttle. Equilibrium occurs in the system if the pressure gradient, .DELTA.p, in the multiway valve matches the force of the spring in the load-sensing regulator. The supply of fluid delivered by the pump is thus automatically adapted to the supply required. The multiway valve upstream of the pertinent consumer is actuated through a hand lever, which is adjustable in proportion to the quantity of the pressure medium, reaches the consumer so that the pressure gradient, .DELTA.p, in the multiway valve always remains constant. Thus, a supply of pressure medium dependent only on the position of the control piston and independent of the load pressure on the consumer always flows through the metering throttle.
Load-sensing regulation will function with several consumers since the maximum load pressure is sensed through a two-way valve chain and is passed to the load-sensing regulator. However, the load-sensing regulation reacts only on the maximum load pressure in the case of several controlled consumers so that the control openings in the multiway valve, which act as metering throttles, of the consumer with a lower load pressure must be newly regulated to compensate for the greater pressure gradients there due to the increased amount delivered by the pump to assure that the speeds of several consumers remain identical even though one consumer is suddenly loaded more heavily than another. Furthermore, at least the ratio of the speed of different consumers to each other is to be maintained if the maximum delivery volume of the pump is exhausted. For this purpose, an additional valve acting as a pressure compensator is located between the pump and the multiway valves. A control pressure chamber of the pressure compensator that is to be loaded in the closing direction is acted upon by the pressure ahead of the multiway valve and its control pressure chamber to be loaded in the opening direction is loaded by the pressure between the multiway valve and the consumer, i.e., by the assigned consumer pressure. An additional control pressure chamber acting in the closing direction is loaded by the pressure of the consumer which is acted upon by the highest load pressure, and an additional control pressure chamber acting in the opening direction is loaded with the pressure in the pump delivery line. Thus, two pressure differences exist. The first pressure difference results from the load pressure of the assigned consumer and the pressure upstream of the multiway valve throttling in the intermediate position, and the second pressure difference results from the opposite switching of the pump delivery pressure and the load pressure of the most highly loaded consumer. It is also possible not to form the pressure differences directly on the pressure compensator and feed the results, e.g., in the form of control pressures to the pressure compensator and allow it to act against a spring force. In any case, the pressure compensators compensate for differences between the pertinent consumer pressure and the highest load pressure. The consumer streams thus behave in accordance with the cross sections of the individual metering throttle openings.
The multiway valves with built-in volume governors distribute the pump stream load independently in relation to the throttle openings on the control piston so long as the stream delivered by the pump matches the sum of the streams absorbed by the consumers. If the sum of the consumer streams exceeds the maximum delivery stream of the pump, the maximum delivery stream is distributed to the consumers in proportion to the opening of the multiway valves assigned to the consumers.
When this system is used, e.g., on an excavating machine, the path line created by two simultaneously controlled operating cylinders of a dredge bucket is maintained at all times, and only when the maximum pump delivery stream is exceeded is the speed of the path line reduced. The ratio of the speeds of the controlled consumers is a function of the ratio of the throttle openings in the actuated multiway valves. The pressure drop is always the same in all multiway valves and corresponds to the regulating pressure difference at the load-sensing regulator. Manual intervention of the multiway valves by the operator is required to effect changes in the ratio of the speeds of the consumers. In particular, great dexterity is required if the path lines are to be traversed with precision.
The present invention proposes a relatively simple controller of the above type, with which changes in the ratios of the speeds of the consumer movements can be made independently of the multiway valves. This is achieved according to the invention by adjusting at least one of the pressure differences on at least one pressure compensator. The equilibrium is thus shifted at the pressure compensator involved and the pressure between the pressure compensator and multiway valve is modified, which results in a change in the pressure drop at the multiway valve and thus a change in the pressure stream and the consumer speed. Accordingly, the invention automatically adjusting regulating pressure gradients are deliberately maintained adjustable at at least one of the pressure compensators in order to be able to control the ratio of the speeds of the consumers.
In an advantageous embodiment of the invention, a pressure compensator is acted upon by a pressure derived from the pressure downstream of the assigned multiway valve and by a pressure derived from the pump pressure in the opening direction and by a pressure derived from the pressure upstream of the multiway valve and by a pressure derived from the highest load pressure of all the consumers in the closing direction. Active surfaces for the pressures are provided in the pressure compensator to which pressure lines are connected. This is accomplished by installing a device that influences the pressure in at least one of the pressure lines. For an arbitrary modification of the delivery stream distribution, one of the four limiting quantities determining the equilibrium at the pressure compensator is deliberately altered to influence the opening and closing forces at the pressure compensator and thus the flow of the pressure medium stream through the metering throttles formed by the control pistons of the multiway valve.
According to another embodiment of the invention, the pressure-influencing device is designed as a pressure-reducing valve. The pressure-reducing valve can be fixed or adjustable. It is particularly favorable if adjustment is by remote control, e.g., electrically, so that the nominal value in the line having the pressure-reducing valve can be modified by the operator. The adjustment can be program-controlled.
Instead of fixed or adjustable pressure-reducing valves, an embodiment of the invention influences the pressure by a throttle located in a line, and an additional throttle with a pressure-limiting valve is located in a discharge line branching off the downstream of the first throttle. This throttle combination serves the same purpose as a pressure-reducing valve.
The device which influences the pressure can be installed in a line carrying the pump pressure which leads to the active surface of the pressure compensator of one of the consumers or in a line carrying the highest consumer pressure which leads to the active surface of the pressure compensator of one of the consumers. Combinations of this arrangement are also possible. In principle, it is possible to influence the amount of pressure medium which flows through the multiway valves by influencing the revertive pressures of the multiway valves, i.e., the pressures upstream of and downstream of the multiway valves.
These as well as other features and advantages of the invention will become more apparent from the detailed specification and the accompanying drawings wherein like reference characters refer to like parts. Although the invention is disclosed in greater detail in the drawings, these drawings are supplied for the purpose of illustration without limiting the invention.